1. Field of Invention
This invention pertains to a cardiac system with an implantable housing that can be selectively rendered to be active or passive. More particularly, the invention describes a cardiac system including housing with a header, a plug and/or a connector with a lead terminating with one or more electrodes and adapted to be inserted into the housing. The structure of the plug or connector defines whether the housing is active or passive.
2. Description of the Prior Art
Implantable cardiac devices are used extensively to provide therapy to patients with various cardiac problems. The therapy from these types of devices usually consists of the application of electrical stimulation pulses to cardiac tissues. Typically, each such device typically consists of sensing circuitry used to sense intrinsic cardiac signals, generating circuitry used to generate electrical stimulation signals, control circuitry used to control the operation of the device, and various auxiliary circuitry used to perform other functions, such as telemetry, data logging, etc. This circuitry is contained in a housing suitable for implantation. The housing further includes a header used to connect the circuitry contained in the housing to one or more leads which extend into, or at least in the vicinity of, the patient's heart and terminate in one or more electrodes. Various header structures are disclosed in U.S. Pat. Nos. 5,545,189; 5,620,477; 5,899,930; 5,906,634; 6,167,314; 6,208,900; and 6,330,477, all incorporated herein by reference.
At least two electrodes are required for sensing, stimulation and some other functions of the device. In many instances, for example, when the housing is implanted pectorally, it is advantageous to have the housing act as one of the electrodes. In these instances, typically at least a portion of the housing's outer surface is exposed and is composed of a conductive material. This portion is then electrically connected to the circuitry within the housing and plays an active part in the operation of the circuitry (i.e., is used to provide stimulation, sensing and/or other functions). Such a housing is often referred to as an ‘active’ housing.
However, an active housing may not be desirable for all locations (e.g., abdominal) because it may be too distant from the heart to be effective, or because it may be, in some instances, adjacent to a muscle that is adversely affected by electrical stimulation.
A housing could be constructed from the start as an active or passive housing by providing an appropriate electrical link between the housing surface and its circuitry. However, this approach is impractical if the decision as to which kind of housing to use is made at the last minute, i.e., just prior to implantation. Since most cardiac devices are programmable, an electrically controlled switch could be used as the link and the decision as to whether to make a housing active or not could be another programming parameter. However, such electrically controlled switches use up space within the housing and add cost and complexity to the electrical circuitry.
U.S. Pat. No. 5,620,477 discloses a housing 12 that can be rendered selectively active and passive using a mechanical element. This housing makes use of a special header having two connector blocks 34, 36. Connector block 34 is connected to an internal circuit while connector block 36 is connected to the conductive surface 16. The housing 12 is rendered active by a plug inserted into the header and having a long connector pin 54 which is positively attached to the connector blocks 34, 36, thereby effectively shorting the two connector blocks to each other. Alternatively, a lead connector is provided with its own connector pin 54. The problem with this approach is that it requires a special design for both the housing header and the plug or lead connector. Thus, this housing cannot be used with standard multi-lead connectors conforming to specific standards, such as an IS-4 quadripolar lead connector.